Memory system

ABSTRACT

A memory system of an embodiment includes a memory device including a first set of cell transistors and a second set of cell transistors; and a controller configured to transmit to the memory device a first instruction and transmit to the memory device a second instruction after reception of a first request without receiving the first request again. The first instruction instructs parallel reads from the first and second sets of cell transistors, and the second instruction instructs a read from the first set of cell transistors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 15/066,255,filed Mar. 10, 2016, which claims the benefit of U.S. ProvisionalApplication No. 62/288,175, filed Jan. 28, 2016, the entire contents ofwhich are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a memory system.

BACKGROUND

A memory system including a NAND flash memory and a controller whichcontrols such a memory is known.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates functional blocks of a memory system of a firstembodiment;

FIG. 2 illustrates functional blocks of a memory device of the firstembodiment;

FIG. 3 illustrates an example of components and connections of a blockof the memory device of the first embodiment;

FIG. 4 illustrates an example of a structure of the block of the memorydevice of the first embodiment;

FIG. 5 illustrates another example of components and connections of theblock of the memory device of the first embodiment;

FIG. 6 illustrates another example of the structure of the block of thememory device of the first embodiment;

FIG. 7 illustrates an example of components and connections of a driverset and a row decoder of the first embodiment;

FIG. 8 illustrates another example of components and connections of thedriver set and the row decoder of the first embodiment;

FIG. 9 illustrates details of the driver set of the first embodiment;

FIG. 10 illustrates the flow of a read of the memory system of the firstembodiment;

FIG. 11 illustrates signals communicated during a multi-plane read inthe memory system of the first embodiment over time;

FIG. 12 illustrates signals communicated during a single plane read inthe memory system of the first embodiment over time;

FIG. 13 illustrates an outline of a read in the memory system of thefirst embodiment;

FIG. 14A illustrates an example of generation of restore data in asecond embodiment;

FIG. 14B illustrates restoration of data with the restore data in thesecond embodiment;

FIG. 15 illustrates signals communicated during a status read in thesecond embodiment over time;

FIG. 16 illustrates information read by a status read command of thesecond embodiment;

FIG. 17 illustrates a part of the flow of a read of the memory system ofthe second embodiment;

FIG. 18 illustrates another part of the flow of the read of the memorysystem of the second embodiment;

FIG. 19 illustrates an outline of a write in the memory system of thesecond embodiment;

FIG. 20 illustrates signals communicated during a multi-plane write inthe memory system of the second embodiment over time;

FIG. 21 illustrates a possible example of storing of data in a memorycontroller during a write;

FIG. 22 illustrates storing of data during a write in the memorycontroller of the second embodiment;

FIG. 23 illustrates a part of the flow of a write of a memory system ofa third embodiment;

FIG. 24 illustrates another part of the flow of the write of the memorysystem of the third embodiment;

FIG. 25 illustrates one state during the write of the memory system ofthe third embodiment;

FIG. 26 illustrates another state during the write of the memory systemof the third embodiment;

FIG. 27 illustrates a possible example of storing of data in a memorycontroller during a write;

FIG. 28 illustrates storing of data during a write in the memorycontroller of the third embodiment;

FIG. 29 illustrates functional blocks of a memory system of a fourthembodiment;

FIG. 30 illustrates a leak word line table of the fourth embodiment;

FIG. 31 illustrates a part of the flow of a write of the memory systemof the fourth embodiment;

FIG. 32 illustrates another part of the flow of the write of the memorysystem of the fourth embodiment;

FIG. 33 illustrates information read by a status read command of thefourth embodiment;

FIG. 34 illustrates voltages of some interconnects during a current leaktest of the fourth embodiment over time;

FIG. 35 illustrates an outline of the write of the memory system of thefourth embodiment;

FIG. 36 illustrates the flow of a read of the memory system of thefourth embodiment;

FIG. 37 illustrates a part of the flow of a write of a memory system ofthe fifth embodiment;

FIG. 38 illustrates another part of the flow of the write of the memorysystem of the fifth embodiment;

FIG. 39 illustrates voltages of some interconnects during a current leaktest of the fifth embodiment over time;

FIG. 40 illustrates the flow of a read of the memory system of the fifthembodiment;

FIG. 41 illustrates voltages of some interconnects during a current leaktests of a sixth embodiment over time; and

FIG. 42 illustrates information read by a status read command of thesixth embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, a memory system includes amemory device including a first set of cell transistors and a second setof cell transistors; and a controller configured to transmit to thememory device a first instruction and transmit to the memory device asecond instruction after reception of a first request without receivingthe first request again. The first instruction instructs parallel readsfrom the first and second sets of cell transistors, and the secondinstruction instructs a read from the first set of cell transistors.

Embodiments will now be described with reference to the figures. In thefollowing description, components with substantially the samefunctionalities and configurations will be referred to with the samereference numerals, and repeated descriptions may be omitted. The entiredescription for a particular embodiment also applies to anotherembodiment unless it is explicitly mentioned otherwise or obviouslyeliminated. Each functional block can be implemented as hardware,computer software, or combination of the both. It is not necessary thatfunctional blocks are distinguished as in the following examples. Forexample, some of the functions may be implemented by functional blocksdifferent from those illustrated below. Furthermore, an illustratedfunctional block may be divided into functional sub-blocks.

Any step in a flow of a method of an embodiment is not limited to anyillustrated order, and can occur in an order different from anillustrated order and/or can occur concurrently with another step.

First Embodiment

(Configuration (Structure))

FIG. 1 illustrates functional blocks of a memory system 1 of the firstembodiment. As illustrated in FIG. 1, the memory system 1 communicateswith a host device 2, and stores data from the host device 2 and readsdata to the host device 2 based on instructions of the host device 2.

The memory system 1 includes a semiconductor memory device 100 and amemory controller 200. The memory device 100 and the memory controller200 may be separate chips, or one chip. The memory controller 200receives commands from the host device 2, and controls the memory device100 based on the received commands. Specifically, the memory controller200 writes data instructed to be written by the host device 2 (hostwrite data) into the memory device 100, and reads data instructed to beread by the host device 2 (host read data) from the memory device 100 totransmit the read data to the host device 2. The memory device 100 is anonvolatile semiconductor memory device, and for example, a NAND flashmemory.

The memory controller 200 includes a host interface 210, an overallcontroller 220, a buffer 230, and a media controller 240. The memorycontroller 200 includes, for example, a processor, such as a centralprocessing unit (CPU), a read only memory (ROM), and a random accessmemory (RAM) as hardware, and it performs a part or all of functions ofthe host interface 210, the overall controller 220, the buffer 230, andthe media controller 240 when firmware (program) stored in the ROM isexecuted by the processor.

The host interface 210 is coupled to the host device 2 through a bus,and manages communications between the memory controller 200 and thehost device 2. The overall controller 220 is implemented by a part offunctions of the processor and the RAM, for example. The overallcontroller 220 controls the whole memory controller 200, controls thebuffer 230 and the media controller 240, and manages cooperation of thebuffer 230 and the media controller 240.

The buffer 230 temporarily stores data. The buffer 230 is implemented bya part of the memory space of the RAM, for example. The media controller240 follows the control of the overall controller 220 to control thememory device 100 and learn the states of the memory device 100. Themedia controller 240 is implemented by a part of the functions of theprocessor and the RAM, for example. The media controller 240 includes areference table 241 and a data restore circuit 242.

The reference table 241 is implemented by a part of the memory space ofthe RAM of the memory controller 200. The reference table 241 indicatesvarious information and includes a translation table of logicaladdresses and physical addresses. The translation table indicates thearea of a physical address in which the latest data assigned a logicaladdress is stored. A logical address is assigned to host write data bythe host device 2, and a physical address identifies an area in thememory space in the memory device 100. The reference table 241 has onlyentries which include invalid data (or, which do not include valid data)when the memory system 1 receives a power supply for the first time foroperation, and entries are updated one by one during operation of thememory system 1. The reference table 241 is stored in the memory device100 when the power supply of the memory system 1 is stopped, and is readfrom the memory device 100 onto the RAM of the memory controller 200upon the next power supply.

The data restore circuit 242 restores data. Restoration of data includesrestoration of lost data, and correction of errors in data.Specifically, the data restore circuit 242 uses host write data togenerate data for restoration of the host write data. The data restorecircuit 242 stores the data for restoration therein, and, morespecifically, in a part of the RAM or in the buffer 230 of the memorycontroller 200. This kind of data is hereinafter referred to as restoredata. The data restore circuit 242 can use specific write and restoredata to restore other write data. Such specific restore data isgenerated from, for example, a total two of a specific first data itemand second data item, can restore the second data item from the firstdata item and the restore data, and can restore the first data item fromthe second data item and the restore data. Such restore data can begenerated by any known methods, and can be generated using, for example,exclusive OR. An example of generation of restore data is described inthe second embodiment.

The data restore circuit 242 adds another type of restore data to hostwrite data. This kind of restore data is a parity. The parity can begenerated by any known methods. The set of specific host write data andthe parity is referred to as an error correction code (ECC) in general.The set of host write data and the parity is written into the memorydevice 100, and this set is hereinafter referred to as the memory writedata. The data restore circuit 242 uses the parity for memory write dataread from the memory device 100 (to be referred to as memory read datahereinafter) to detect errors of the memory read data, and, when errorsare detected, it attempts to correct the errors to obtain correct memoryread data.

The media controller 240 is coupled to the memory device 100 through abus. The bus is a NAND bus when based on an example where the memorydevice 100 is the NAND flash memory, and the following description isbased on the example of the NAND bus. The NAND bus transmits signals/CE, CLE, ALE, /WE, /RE, RB, and I/O. The signal /CE enables the memorydevice 100, and, when the memory device 100 includes plural memorydevices 100 (chips of memory devices), it is enabled in order to selectone memory device 100, for example. The signals CLE and ALE notify thememory device 100 that the signal I/O flowing into the memory device 100in parallel with the signals CLE and ALE is a command and an address,respectively. An asserted signal /WE instructs the memory device 100 totake in the signal I/O flowing into the memory device 100 in parallelwith the signal /WE. The sign “/” at the beginning of the name of asignal indicates that the signal is asserted when it is low. The signal/RE instructs the memory device 100 to output the signal I/O. The signalRB indicates whether the memory device 100 is in a ready state or busystate, and indicates the busy state when it is low. The memory device100 accepts commands from the memory controller 2 in the ready state,and does not accept commands from the memory controller 2 in the busystate. The signal I/O has a width of, for example, eight bits, issubstantial data, and includes commands (CMD), memory write data ormemory read data (DAT), address signals (ADD), status data (STA), etc.

The memory device 100 has functional blocks illustrated in FIG. 2. Asillustrated in FIG. 2, the memory device 100 includes plural planes PB(PB0 and PB1), a driver set 11, a sequencer 12, a register 13, and acharge pump (voltage generator) 14. Each plane PB includes a cell array21, a row decoder 22, a sense amplifier 23, a data latch 24, and acolumn decoder 25.

The cell array 21 includes blocks BLK (BLK0, BLK1, . . . ). Differentplanes PB include a set of blocks BLK of the same addresses (IDs).Same-address blocks BLK of the different planes PB are distinguished byspecifying a plane PB. Each block BLK includes plural NAND strings STR(STR0, STR1, . . . ). Each string STR includes plural memory cells (notshown). The memory space of a particular plurality of memory cells makesone or more pages. The cell array 21 is also provided with variousinterconnects.

The sequencer 12 receives the commands CMD and controls the driver set11, the charge pump 14, the sense amplifiers 23, and the data latches 24in accordance with the sequence based on the commands CMD.

The charge pump 14 generates various voltages (potentials) from thepower voltage in accordance with instructions of the sequencer 12.

The driver set 11 receives a row address signal in an address signalADD. A row address signal specifies a row address. The driver set 11receives various potentials from the charge pump 14, and supplies therow decoder 22 with various potentials from the charge pump 14 based onthe row address signals. The driver set 11 includes plural drivers,which will be described later.

The row decoder 22 receives the row address signal in the address signalADD, and selects one block BLK based on the row address signal. To aselected block BLK in a selected plane PB0 and/or PB1, potentials fromthe driver set 11 are transferred.

The sense amplifier 23 reads data from the memory cells, and writes datain the memory cells in accordance with the control of the sequencer 12.The data latch 24 includes plural data latch units, stores data to thesense amplifier 23, and stores data from the sense amplifier 23. Eachdata latch unit can store data of one-page size.

The column decoder 25 receives a column address signal in an addresssignal ADD. A column address signal specifies a column. The columndecoder 25 selects a column based on the column address signal, andcontrols the data latch 24.

The register 13 stores various data and transmits the stored data to thememory controller 200 in accordance with instructions of the sequencer12. The data includes the status data STA. The status data STA indicatesvarious states of the memory device 100.

The planes PB includes respective sets of a cell array 21, a row decoder22, a sense amplifier 23, a data latch 24, and a column decoder 25, andcan separately operate (read, write, or erase data, etc.) in parallel.

Each block BLK has components and connections illustrated in FIG. 3, andhas the structure illustrated in FIG. 4. As illustrated in FIGS. 3 and4, each string STR includes n+1 cell transistors MT (MT0 to MTn) andselect gate transistors SDT and SST, which are coupled in series. n is anatural number. Each cell transistor MT includes a tunnel insulator TIon a p-type well region pw in a semiconductor substrate sub, a chargestorage film CI on the tunnel insulator TI, an inter-gate insulator (notshown) on the charge storage film CI, a control gate electrode CG (wordline WL) on the inter-gate insulator, and source or drain areas SD. Thecharge storage film CI is insulated from around, and is, for example, afloating gate electrode (FG) or may be an insulator. Each celltransistor MT can store data in a nonvolatile manner based the thresholdvoltage varying based on the quantity of charge (the number ofelectrons) in the charge storage film CI. In a write the thresholdvoltage of the cell transistor MT is adjusted by injecting electrons,and in a read it is determined whether the threshold voltage of the celltransistor MT exceeds a reference (read voltage Vcgr).

The select gate transistor SST is coupled between a source line SL andthe cell transistor MT0, and the select gate transistor SDT is coupledbetween one bit line BL and the cell transistor MTn. Data in celltransistors MT in the block BLK are erased together.

For each p (p being zero or a natural number smaller than or equal ton), respective control gate electrodes CG of respective cell transistorsMTp of the strings STR are coupled to a word line WLp in common. Thecell transistors MT coupled to the same word line WL make a cell unitCU. The data of cell transistors MT of one cell unit CU are written andread together. The memory space of one cell unit CU includes one or morepages. When a particular cell unit CU stores data of the one-page size,each cell transistor in that cell unit CU stores one bit data. When aparticular cell unit CU stores data of a two-page size, each celltransistor in that cell unit CU stores two bit data. The same holds truefor cases of three pages or more.

Respective gates of respective select gate transistors SST of thestrings STR are coupled to a select gate line SGSL. Respective gates ofrespective select gate transistors SDT of the strings STR are coupled toa select gate line SGDL.

Alternatively, each block BLK has components and connections illustratedin FIG. 5, and has the structure illustrated in FIG. 6. In the FIG. 5configuration, plural strings STR are coupled to one bit line BL in eachblock BLK. One string STR coupled to each bit line BL belongs to onestring unit SU, and each block BLK includes string units SU0 to SUk. kis a natural number and is three as an example in the followingdescription. The configuration in which one string unit SU is includedin one block BLK corresponds to the FIG. 3 configuration.

Each bit line BL is coupled to one string STR from each of the fourstring units SU0 to SU3 in each block BLK.

Each string STR includes a select gate transistor SSTb (SSTb0, SSTb0,SSTb2, or SSTb3), a select gate transistor SST (SST0, SST1, SST2, orSST3), memory cell transistors MT0 to MTn, and a select gate transistorSDT (SDT0, SDT1, SDT2, or SDT3). The transistors SSTb, SST, and MT andSDT are coupled in series between the source line SL and one bit line BLin this order.

Strings STR respectively coupled to different bit lines BL on aone-to-one basis make one string unit SU. In each string unit SU, thegates of the cell transistors MTp are coupled to a word line WLp foreach p. The set of the cell transistors MT which share a word line WL inone string unit SU makes a cell unit CU. In each block BLK, the wordlines WLp in different string units SU are also coupled to each other.

The select gate transistors SDTq, SSTq, and SSTbq belong to a stringunit SUq, where q is either zero or a natural number lower than or equalto k (=3).

For each q, respective gates of respective select gate transistors SDTqof strings STR of the string unit SUq are coupled to a select gate lineSGDLq. For each q, respective gates of respective select gatetransistors SSTq of strings STR of the string unit SUq are coupled to aselect gate line SGSLq. For each q, respective gates of respectiveselect gate transistors SSTbq of strings STR of the string unit SUq arecoupled to a select gate line SGSLbq.

The select gate lines SGSL of two or more of the string units SU in oneblock BLK may be coupled to each other. The select gate lines SGSbL oftwo or more of the strings unit SU in one block may also be coupled toeach other.

The circuit illustrated in FIG. 5 can be implemented by the structureillustrated, for example in FIG. 6. FIG. 6 illustrates the example ofn=7. As illustrated in FIG. 6, a string STR is disposed above thesubstrate sub. The well area pW is disposed in the surface of thesubstrate sub, and a semiconductor pillar SP is disposed on the wellarea pW along the d3 axis. The side of the semiconductor pillar SP iscovered with a tunnel insulator TI. The side of the tunnel insulator TIis covered with a charge storage film CI. The charge storage film CI isan insulator or conductor, and has a side covered with a block insulatorBI. The semiconductor pillar SP serves as a current path of a stringSTR, and provides the area in which the channels for the celltransistors MT and select gate transistors SDT, SST, and SSTb areformed.

Above the well area pW, the select gate lines SGSbL and SGSL, the wordlines WL (WL0 to WL7), and the plural select gate lines SGDL spreadalong the d12 plane. The d12 plane is the plane which consists of the d1axis and d2 axis. The select gate lines SGDL are coupled to each other(not shown). The select gate lines SGSbL and SGSL, the set of the wordlines WL0 to WL7, and the set of the select gate lines SGDL are lined upin this order along the d3 axis with an interval. The select gate linesSGSbL and SGSL, the word lines WL, and the select gate line SGDL are incontact with the block insulator BI.

Of the semiconductor pillar SP, the tunnel insulator TI, the chargestorage film CI, and the block insulators BI, the section which crosseswith the select gate line SGSbL serves as the select gate transistorSSTb, the section which crosses the select gate line SGSL serves as theselect gate transistor SST, and the section which crosses a word line WLserves as a cell transistor MT.

The transistors SSTb, SST, MT, and SDT which are lined up along the d3axis correspond to the transistors included in one string STR.

A bit line BL is disposed above, along the d3 axis, the semiconductorpillar SP. The bit line BL extends along the d1 axis, and plural bitlines have an interval along the d2 axis. One bit line BL is coupled tothe tops of strings STR via plugs VP1 and VP2.

Plural strings STR illustrated in FIG. 6 are disposed in differentcoordinates on the d2 axis. Such strings STR disposed in differentcoordinates on the d2 axis correspond to strings STR included in onestring unit SU.

In the surface area of the well area pW, a diffusion layer of n+ typeimpurities nd is further provided. The diffusion layer nd is coupled tothe bottom of a contact plug CP1. The top of the contact plug CP1 iscoupled to a source line SL.

As described above, the select gate lines SGDL, SGSL, and SGSbL, theword lines WL, and the source line SL are coupled to the driver set 11through the row decoder 22, and driven by the drive set 11. The detailsof the driver set 11 differ in the case where the blocks BLK have theFIG. 3 structure, which will be referred to as a single string typehereinafter, and the case where they have the FIG. 5 structure, whichwill be referred to as a multi-string type. FIGS. 7 and 8 illustrate thecomponents and connections of the row decoder 22 and the driver sets 11for the single string type and the multi-string type, respectively. Thedifferences are in components for selecting one string unit SU in oneblock BLK in the multi-string type structure.

FIGS. 7 and 8 also illustrate the charge pump 14. The charge pump 14includes plural pump units 141 a, 141 b, . . . , each of which cangenerate a potential independently from another.

The row decoder 22 includes a set of plural block decoders 22 a (22 a 0,22 a 1, . . . ) for the respective blocks BLK. In addition, asillustrated in FIGS. 7 and 8, only in one block BLK selected by oneblock decoder 22 a, the select gate lines SGDL, SGSL, and SGSbL and theword lines WL (WL0 to WLn) are coupled to the interconnects SGD, SGS,SGSb, and CG (CG0 to CGn) through transistors XFR, respectively. In FIG.7, the interconnects SGD and SGS are coupled to drivers SGDdrv andSGSdrv, respectively, and the interconnects CG0 to CGn are coupled todrivers CGdrv0 to CGdrvn, respectively. In FIG. 8, the interconnects CG0to CGn are coupled to drivers CGdrv0 to CGdrvn, respectively, andfurther, for each q, the interconnect SGDq is coupled to a driverSGDdrvq, the interconnect SGSq is coupled to a driver SGSdrvq, and theinterconnect SGSbq is coupled to a driver SGSbdrvq. The source line SLis coupled to a driver SLdrv.

In FIG. 8, the drivers SGDdrv, SGSdrv, and SGSbdrv for a selected stringunit SU apply various potentials to the interconnects coupled theretoduring a read, write or erase of data. In contrast, the drivers SGDdrv,SGSdrv, and SGSbdrv for unselected string units SU output the groundpotential VSS (=0V). In this way, only one selected string unit SU iscoupled to the bit lines BL and/or source line SL.

As illustrated in FIG. 9, the driver set 11 is also shared by the pluralplanes PB. Specifically, the interconnect CG0 is coupled to each blockBLK of the plane PB0 through the transistors XFR of each block decoder22 a for the plane PB0, and coupled to each block BLK of the plane PB1through the transistors XFR of each block decoder 22 a for the planePB1. The same applies to the interconnects CG1 to CGn, SGD0 to SGD3,SGS0 to SGS3, and SGSb0 to SGSb3. Selection of one or both of the planesPB is performed by the block decoders 22 a. Specifically, in one or bothof the planes PB selected by the row address signal, the block decoders22 a for the selected block BLK turn on the transistors XFR thereof.

Based on such sharing of one component and having common addresses byplural components, specification of one cell unit CU includesspecification of one or both planes PB, one block BLK, and one word lineWL. Furthermore, in the multi-string structure, specification of onecell unit CU further includes specification of one string unit SU.

(Operation)

Referring to FIGS. 10 to 13, a read in the memory system of the firstembodiment will be described. The following description is based on theexample where each cell transistor MT of a mentioned cell unit CU storesone-bit data, i.e., the example of storing data of one-page size percell unit CU. Based on this example, specification of a particular pageequals specification of one cell unit CU, and by extension,specification of one word line WL.

FIG. 10 illustrates the flow of a read of the memory system of the firstembodiment. When the host device 2 instructs (or, requests) a read ofdata to the memory system 1 and this instruction leads to a read of datafrom plural planes PB, which will be referred to as a multi-plane readhereinafter, the FIG. 10 flow starts. As a specific example, the overallcontroller 220 interprets the read instruction from the host device 2,and determines to read host read data HA0 and HA1 from the planes PB0and PB1, respectively. The host read data HA0 and the parity thereofmake memory read data A0, and the host read data HA1 and the paritythereof make memory read data A1. The memory read data A0 and A1 arestored in the planes PB0 and PB1, respectively. The instruction from theoverall controller 220 is received by the media controller 240, and theFIG. 10 flow starts. The FIG. 10 flow occurs after the instruction totrigger the FIG. 10 flow and before the performance (or, completion) ofanother additional instruction (or, request) from the host device 2 bythe memory system 1, for example. Specifically, the flow occurs as aresponse to reception of the read instruction of the host read data HA0and HA1. In addition, the flow occurs as a response to reception of oneread instruction of the host read data HA0 and HA1 from the host device2. In other words, the flow is performed without reception of two ormore identical instructions from the host device 2.

The following description is based on the example of the multi-planeread from the two planes PB. The read for three or more planes PB can,however, be similarly performed by extension of the principle describedin the following. This aspect is applicable to other embodiments thatfollow.

In step S1, the media controller 240 (memory controller 200) refers tothe reference table 241 to learn the addresses of the pages storing thememory read data A0 and A1. In the ongoing example, the memory read dataA0 and A1 are stored in pages of cell units CU coupled to a word lineWLx (x being a natural number below 0 or n) of the same address in thesame-address blocks BLK in the planes PB0 and PB1.

The media controller 240 learns that the instructed read is amulti-plane read because the memory read data A0 and A1 are stored inthe cell units CU of two planes PB. The specification of the selectedword line WLx in a particular plane PB includes specification of oneplane PB, one block BLK, and one word line WLx. Furthermore, when theblocks BLK are of the multi-string type, the specification of one cellunit CU further includes specification of one string unit SU.

In step S2, the media controller 240 instructs the multi-plane read fromthe cell units (selected cell units) CUx of the word line WLx of theplanes PB0 and PB1 to the memory device 100. The instruction of themulti-plane read instructs parallel reads from the instructed pluralplanes PB.

When the multi-plane read instruction is received by the memory device100, the sequencer 12 in step S3 controls the driver set 11, and thesense amplifier 23, the data latch 24, and the column decoder 25 of theplanes PB0 and PB1 to read the memory read data A0 and A1 from the cellunits CUx.

The memory read data A0 and A1 are transmitted from the memory device100 to be received by the media controller 240. The received memory readdata A0 and A1 may include errors.

In step S4, the media controller 240 controls the data restore circuit242 to detect errors of the memory read data A0 and A1, and, if any, ittries to correct them to obtain correct memory read data A0 and A1. Whenone or both of correct memory read data A0 and A1 are obtained (Nobranch), the flow shifts to step S5.

When both correct memory read data A0 and A1 are obtained, the host readdata HA0 and HA1 are obtained, and they are transmitted to the hostdevice 2 by the overall controller 220 in step S5. When only memory readdata A0 or A1 is obtained, the media controller restores from theobtained memory read data A0 (or A1) the memory read data A1 (or A0).The restoration can be performed by various methods. Examples of themethods include use of a product code. The product code is known bypersons skilled in the art. Based on the ongoing example, the generationof a product code includes using the string of bits from a set of memorywrite data (sets of host write data and parity thereof) to generateanother parity. With the restoration, both host read data HA0 and HA1are obtained. After step S5 is completed, the FIG. 10 flow ends.

In contrast, when the error correction of both memory read data A0 andA1 fail in step S4 (Yes branch), the flow shifts to step S7. In thesteps from step S7, the media controller 240 tries a read from theselected cell units CU of the planes PB0 and PB1 and error correctionfor each plane PB separately. The details of operation are similar tothat in the multi-plane read. A read from any plane PB can be performedfirst.

In step S7, the media controller 240 instructs a single plane read fromthe cell unit CUx of the plane PB0 to the memory device 100. When theinstruction is received by the memory device 100, the sequencer 12 readsthe memory read data A0 from the cell unit CUx of the plane PB0 in stepS8. The memory read data A0 is transmitted from the memory device 100 tobe received by the media controller 240.

In step S9, the media controller 240 tries to obtain the correct memoryread data A0. When the correct data is obtained (No branch), the hostread data HA0 is obtained, and the flow shifts to step S10.

In step S10, the media controller 240 restores the memory read data A1from the memory read data A0. With the restoration, both host read dataHA0 and HA1 are obtained, and the overall controller 220 transmits thehost read data HA0 and HA1 to the host device 2, where the flow ends.

In contrast, when the errors are uncorrectable in step S9 (Yes branch),the media controller 240 instructs a single plane read from the cellunit CUx of the plane PB1 to the memory device 100 in step S12. When theinstruction is received by the memory device 100, the sequencer 12 readsthe memory read data A1 from the cell unit CUx of the plane PB1 in stepS13. The memory read data A1 is transmitted from the memory device 100to be received by the media controller 240.

In step S14, the media controller 240 tries to obtain correct memoryread data A1. When the correct data is obtained (No branch), the hostread data HA1 is obtained, and the flow shifts to step S15.

In step S15, the media controller 240 restores the memory read data A0from the memory read data A1. With the restoration, both host read dataHA0 and HA1 are obtained, and the overall controller 220 transmits thehost read data HA0 and HA1 to the host device 2, where the flow ends.

In contrast, when the errors are uncorrectable in step S14 (Yes branch),the flow shifts to step S16. In step S16, the overall controller 220notifies the host device 2 that the read of the host read data HA0 andHA1 failed, and the flow ends. Alternatively, in step S16, the mediacontroller 240 can perform a retry read to each of the planes PB0 andPB1. A retry read refers to a read with a read voltage larger or smallerthan the read voltage used, for example, in the read by the lastmulti-plane read instruction (in step S2). By one or more retry reads,the memory read data A0 and A1 may be obtained.

FIG. 11 illustrates signals communicated between the memory controller200 and the memory device 100 during one multi-plane read by the memorysystem 1 of the first embodiment over time. The communication in FIG. 11may occur in step S2 of FIG. 10.

As illustrated in FIG. 11, the media controller 240 keeps asserting thesignal /CE (or, maintains the signal at low), and keeps negating thesignal /RE (maintains the signal at high) over the period illustrated inFIG. 11.

The media controller 240 transmits a command and an address signal forone of the two planes PB0 and PB1 to the memory device 100. Any plane PBcan precede. The process for the plane PB0 precedes in the followingexample.

The media controller 240 asserts (or, makes high) the signal CLE, andtransmits a write command 00h to the memory device 100 while the signalCLE is asserted. Moreover, the media controller 240 asserts (or, makeslow) the signal /WE while the write command 00h is transmitted. Thus,the transmission of a command includes the transmission of the assertedsignal CLE, the transmission of the command during the transmission ofthe asserted signal CLE, and the transmission of the asserted signal /WEduring the transmission of the command.

Subsequently, the media controller 240 asserts (or, makes high) thesignal ALE, transmits an address signal (or, set of sections AD1 to AD5)while the signal ALE is asserted, and asserts the signal /WE during thetransmission of each of sections AD1 to AD5 of the address. The addresssignal is transmitted by five cycles, for example. The first two are acolumn address signal and the last three are a row address signal. A rowaddress signal specifies one plane PB, one block BLK, and one word lineWL. A row address signal further specifies one string unit SU when theblock BLK is of the multi-string type.

Thus, the transmission of an address signal includes the transmission ofthe asserted signal ALE, the transmission of the address signal duringthe transmission of the asserted signal ALE, and the transmission of theasserted signal /WE during the transmission of each section of theaddress signal.

The media controller 240 transmits a command 32h to the memory device100 after it transmits the address signal for the plane PB0. The command32h instructs not to start and to suspend the read specified by thecommand 00h and the following address signal, and indicates a subsequentinstruction will follow.

When the memory device 100 receives the command 32h, it makes the signalR/B low to notify a busy state to the memory controller 200.

When the busy state ends, the media controller 240 transmits the readcommand 00h and the address signal (AD1 to AD5) for the plane PB1 to thememory device 100. The address in the address signal for the plane PB0and that for the plane PB1 of the target of the multi-plane read specifythe same address except for the address of the plane. After the mediacontroller 240 transmits the address signal for the plane PB1, ittransmits a command 30h to the memory device 100. The command 30hinstructs execution of the suspended instruction (i.e., the read fromthe plane PB0), and the instruction just prior to the command 30h (i.e.,the read from the plane PB1).

When the memory device 100 receives the command 30h, it executes theinstructions. The execution of the instructions corresponds to theexecution of step S3 of FIG. 10, for example. The memory device 100notifies the busy state to the memory controller 200 during theexecution of instructions. The busy time corresponds to the read timetR.

FIG. 12 illustrates signals communicated between the memory controller200 and the memory device 100 during a single plane read by the memorysystem 1 of the first embodiment over time. The communication in FIG. 12may occur in steps S7 and S12 of FIG. 10. The details are similar tothose of the multi-plane read. They differ in that the media controller240 issues the command 30h after it transmits the address signal for onetarget plane PB.

FIG. 13 illustrates the outline of a read in the memory system 1 of thefirst embodiment. The operation illustrated in FIG. 13 may occur by theexecution of the FIG. 10 flow. FIG. 13(a) corresponds to steps S2, S3,and the Yes branch of S4 of FIG. 10. As an example, the word line WLx ofa particular plane (for example, the plane PB0) and an adjacent wordline WLx−1 are unintentionally short-circuited. In contrast, the wordline WLx of another plane PB1 is not short-circuited with an adjacentword line WLx−1.

Assume that, with the word line WLx short-circuited in this way, themedia controller 240 performs a multi-plane read from the cell units CUxbased on the instruction from the host device 2. Such a situation mayoccur after writes without a status read after every write, for example.The memory controller 200 can instruct the memory device 100 to transmitthe status about the success or failure of a write after the write.Successive writes of data without such a status read can, however, beperformed, and in such a case, it will turn out that the read-targetword line WLx is short-circuited for the first time when the multi-planeread is performed. In addition, the word line WLx may be short-circuitedafter the status read due to some reasons.

The multi-plane read results in failure of reads from the cell units CUxof the planes PB0 and PB1. This is because a current leak from the wordline WLx disables the word line WLx to be applied with a read voltageVcgr. The failure of read can be determined by the data restore circuit242 when it determines that the memory read data A0 from the selectedcell unit CU of the word line WLx of the plane PB0 includesuncorrectable errors.

The read from the word line WLx of the plane PB1 also fails. The wordlines WL of a particular address of different planes PB are not coupledto each other. For this reason, the short circuit between the word linesWLx and WL31 1 of the plane PB0 does not necessarily influence the planePB1. In multi-plane read, however, the planes PB0 and PB1 are specified,which turn on the transfer transistors XFR of the selected block BLK ofthe plane PB0 and those of the selected block BLK of the plane PB1. Theword line WLx of plane PB1 is, in turn, electrically coupled to that ofthe plane PB0 through the transfer transistors XFR. For this reason, themulti-plane read results in failure of the read from the cell unit CUxof the word line WLx also in the plane PB1.

Thus, the multi-plane read fails also in the read in the plane PB1,which does not include a short circuit of the word line WLx. If eachword WLx of the two planes PB0 and PB1 is actually short-circuited withan adjacent word line WLx−1 (or WLx+1), reads from the cell units CUx ofthe planes PB0 and PB1 actually fail. Such a phenomenon, however, hardlyoccurs in terms of probability, and such a short circuit is unlikely toactually occur. For this reason, it is assumed that the multi-plane readfrom the cell units CUx with the word line WLx of one plane PBshort-circuited resulted in the failure of the reads of the memory readdata A0 and A1 of both planes PB0 and PB1.

Based on such assumption, as illustrated in FIGS. 13(b) and (c), thememory controller 200 performs separately the read from the cell unitCUx of the plane PB0 and that from the cell unit CUx of the plane PB1.

FIG. 13(b) corresponds to steps S7 and S8, and the Yes branch of S9 ofFIG. 10. As illustrated in FIG. 13(b), the media controller 240 performsa single plane read from the cell unit CUx of the plane PB0. The readdata by this single plane read is determined to be error-uncorrectableby the data restore circuit 242.

FIG. 13(c) corresponds to steps S12 and S13, and the No branch of S14 ofFIG. 10. As illustrated in FIG. 13(c), the media controller 240 performsa single plane read from the cell unit CUx of the plane PB1. With thissingle plane read, data is read correctly.

(Advantages)

According to the first embodiment, when the errors of both data from theplane PB0 and that from the plane PB1 read by a multi-plane read areuncorrectable, the memory controller 200 performs single plane reads tothe planes PB0 and PB1 separately. As a result, when the data read fromthe two planes PB by the multi-plane read fails due to a short circuitof a word line WLx of one plane PB, data can be read from the cell unitCUx of the word line WLx of the other plane PB.

Second Embodiment

The second embodiment is similar to the first embodiment, and relates tooperations during writes with status reads.

In the second embodiment, the memory system 1 has the same functionalblocks as the memory system 1 of the first embodiment. In contrast, thememory controller 200 is configured to perform the operations describedin the following in the second embodiment. The blocks BLK of the secondembodiment are of the single string type.

FIG. 14A illustrates an example of generation of restore data in thesecond embodiment, and FIG. 14B illustrates restoration of data with therestore data in the second embodiment. The media controller 240 performsthe operation illustrated in FIG. 14A to prepare a multi-plane write tothe memory device 100. First, the media controller 240 generates memorywrite data Z0 and Z1, which will be written in the planes PB0 and PB1,respectively.

The media controller 240 further controls the data restore circuit 242to use a total of two bits of the same position in the memory write dataZ0 and Z1 to generate the information for restoring one of the two bitsfrom the other. As an example, the media controller 240 generates data(bit) by applying the exclusive OR (XOR) to a total two of the firstbits from the memory write data Z0 and Z1, and stores the generated data(bit) in the buffer 230. Similarly, the data restore circuit 242generates the exclusive OR of each of all the remaining bits. Thethus-generated set of bits of exclusive OR is restore data RZ01. Therestore data RZ01 has the same size as the memory write data Z0 or Z1.

As illustrated in FIG. 14B, when one of the memory read data Z0 and Z1is lost (for example, memory read data Z1) during a read, the other readdata Z0 and the restore data RZ01 can be used to restore the read dataZ1. Specifically, the exclusive OR of two bits in the same position ofthe memory read data Z0 and the restore data RZ01 can restore thecorresponding bit in the read data Z1. The restore data may be generatedby any method as long as it allows one of associated two data items fromthe other.

FIG. 15 illustrates signals communicated between the memory controller200 and the memory device 100 during a status read used in the secondembodiment over time. As illustrated in FIG. 15, the memory controller200 transmits a status read command XXh to the memory device 100. Whenthe memory device 100 receives the status read command, it stores in theregister 13 various kinds of status data about the instructions justprior to the reception of the command. Then, when the memory controller200 asserts the signal /RE, the memory device 100 responds to this andtransmits the status data to the memory controller 200 from the register13.

FIG. 16 illustrates an example of the information read by the statusread command XXh. More specifically, FIG. 16 illustrates the informationread by the status read command which follows a write instruction tocell units CU (including the case where the cell units belong to thedifferent planes PB). As illustrated in FIG. 16, each bit of the signalI/O indicates a corresponding one of various statuses. I/O[0] indicateswhether the last instruction (i.e., write instruction) is success orfailure with a “0” bit and “1” bit, respectively. I/O[1] is used whenthe status is read before completion of transmission of all write datato the read-target cell units CU to the memory device 100, and indicatesthe success or failure of reception of the last write data for the cellunit CU by the memory device 100.

FIGS. 17 and 18 illustrate the flow of a write of the memory system ofthe second embodiment. When the host device 2 instructs a write to thememory system 1 and the instruction leads to data writes to two or morecell units CU of the plural planes PB0 and PB1, which will be referredto as a multi-plane write hereinafter, the flow of FIGS. 17 and 18starts. As an example, the overall controller 220 interprets the writeinstruction from the host device 2, and determines that it willrespectively write host write data HA0 and HA1 into the same-addresscell units CUx of the planes PB0 and PB1 and respectively write hostwrite data HB0 and HB1 into other cell units CU of the planes PB0 andPB1. The overall controller 220 instructs the determined write to themedia controller 240. The reception of the instruction by the mediacontroller 240 triggers the flow of FIGS. 17 and 18. The flow of FIGS.17 and 18 occurs after the instruction to trigger the flow of FIGS. 17and 18 and before the performance (or, completion) of another additionalinstruction (or, request) from the host device 2 by the memory system 1,for example. Specifically, the flow occurs as a response to reception ofthe write instruction of the host write data HA0, HA1, HB0, and HB1. Inaddition, the flow occurs as a response to reception of one writeinstruction of the host write data HA0, HA1, HB0, and HB1 from the hostdevice 2. In other words, the flow is performed without reception of twoor more identical instructions from the host device 2.

In step 21, the media controller 240 refers to the reference table 241to determine cell units CU which will have the host write data HA0, HA1,HB0, and HB1 written, and reflects the result of the determination inthe reference table 241. Specifically, the media controller 240 refersto the reference table 241 to find physical addresses which do not havedata written, i.e., which do not have logical addresses assigned. Themedia controller 240 then updates the reference table 241 so that afound physical address and the host write data HA0 are associated, andanother found physical address and the host write data HA1 areassociated. Because of the multi-plane write, the host write data HA0and HA1 are assigned the addresses of word lines WLx of same-addressblocks BLK of the planes PB0 and PB1, respectively. Similarly, the mediacontroller 240 assigns the host write data HB0 and HB1 to the addressesof word lines WLx+1 of same-address blocks BLK of the planes PB0 andPB1, respectively.

In step S22, the media controller 240 adds a parity to the host writedata HA0 to generate memory write data A0, and adds a parity to the hostwrite data HA1 to generate memory write data A1. The media controller240 further generates restore data RA01 for the memory write data A0 andA1, and stores the same in the buffer 230.

In step S23, the media controller 240 instructs a write of the memorywrite data A0 and A1 to cell units CUx of same-address blocks BLK of theplanes PB0 and PB1 (or, instructs a multi-plane write) to the memorydevice 100. Even after the transmission of the multi-plane writeinstruction, the buffer 230 follows the instruction of the overallcontroller 220 to maintain the memory write data A0 and A1 and therestore data RA01. The storing of the memory write data A0 and A1continues, for example, until the media controller 240 confirms that thememory write data A0 and A1 are correctly written into the memory device100 with a subsequent read. In contrast, restore data RA01 is storeduntil confirmation of a success of the write which triggers the flow ofFIGS. 17 and 18, i.e., the write of the host write data HA0, HA1, HB0,and HB1 in the ongoing example.

When the multi-plane write instruction is received by the memory device100, the sequencer 12 in step S24 controls the driver set 11, and thesense amplifiers 23, the data latches 24, and the column decoders 25 ofthe planes PB0 and PB1, to write the memory write data A0 and A1 intorespective cell units CUx of the planes PB0 and PB1, respectively. Uponcompletion of the writes, the memory device 100 shifts to the readystate. The shift to the ready state is irrelevant to the result ofwhether the writes succeed and does not necessarily indicate a successof the writes.

After the transmission of the multi-plane write instruction in step S23,the media controller 240 further reads the status of the memory device100 in step S25. To this end, the media controller 240 transmits thestatus read command to the memory device 100 after a lapse of aparticular time after the transmission of the multi-plane writeinstruction. The status read is not accepted by the memory device 100during the busy state of the memory device 100. The media controller 240repeatedly issues the status read command with a particular intervaluntil the memory device 100 shifts to the ready state to receive thestatus read command.

When the result of the status read indicates a success, the mediacontroller 240 in step S27 stops storing the memory write data A0 and A1in the buffer 230, and releases the memory space of the buffer 230. Thememory write data A0 and A1 may be erased, or be in a state where it canbe overwritten by other data. Assume that in the ongoing example themulti-plane write to the cell units CUx succeeds for simplification ofthe description.

In step S28, as in step S22, the media controller 240 adds a parity tothe host write data HB0 to generate memory write data B0, and adds aparity to the host write data HB1 to generate memory write data B1. Themedia controller 240 further generates restore data RB01 for the memorywrite data B0 and B1, and stores the same in the buffer 230. Thegeneration of the memory write data HB0 and HB1 and the restore dataRB01 only need to complete from after step S21 before step S29, and maybe performed in parallel to one or more of steps S22, S23, S24, S25, andS27.

In step S29, as in step S23, the media controller 240 instructs a writeof the memory write data B0 and B1 into cell units CUx+1 of the planesPB0 and PB1 to the memory device 100. Even after the transmission of themulti-plane write instruction, the buffer 230 maintains the memory writedata B0 and B1 and restore data RB01.

When the multi-plane write instruction is received by the memory device100, the sequencer 12 in step S31 writes the memory write data B0 and B1into respective cell units CUx+1 of the planes PB0 and PB1,respectively, as in step S24.

In step S32, the media controller 240 reads the status of the memorydevice 100. When the result of the status read indicates a success (Yesbranch), the flow shifts to step S33. In step S33, the media controller220 stops storing the memory write data B0 and B1 in the buffer 230.Moreover, the media controller 240 notifies the completion of theinstruction to the host device 2. Then, the flow ends.

In contrast, the determination of write failure in step S32 (No branch)may occur when, for example, the word lines WLx+1 and WLx becomeshort-circuited during the write into the cell unit CUx+1 of the planesPB0 and PB1 in step S31. The short circuit may have made the memory readdata A0 or A1 of the cell units CUx unreadable. For this reason, stepsS34, S35, and S37 are performed based on the write failure determinationin step S32 in order to try to obtain the memory read data A0 and A1 ofthe cell units CUx.

Steps S34, S35, and S37 are the same as step S2, S3, and S4 of FIG. 10,respectively. Specifically, in steps S34, S35, and S37, the mediacontroller 240 and the sequencer 12 try to obtain the correct memoryread data A0 and A1 from the cell units CUx of the planes PB0 and PB1.

When both correct memory read data A0 and A1 are obtained in step S37(No branch), it results in the memory read data A0 and A1 stored in thebuffer 230. The No branch of step S37 may occur when the failure of themulti-plane write in step S31 does not result from a short circuit ofthe word line WLx+1.

In contrast, when in step S37 obtaining of both correct memory read dataA0 and A1 fails (Yes branch), steps S41, S42, and S43 are performed. Theadvance of the flow to the Yes branch of step S37 may occur when thefailure of multi-plane write in step S31 results from a short circuit ofword line WLx+1. Steps S41, S42, and S43 are the same as steps S7, S8,and S9 of FIG. 10, respectively. Specifically, the media controller 240and the sequencer 12 try to obtain the correct memory read data A0 fromthe cell unit CUx of the plane PB0 in steps S41, S42, and S43. When instep S43 the correct memory read data A0 is obtained (No branch), theflow shifts to step S45. The shift of the flow to step S45 may occurwhen the failure of the multi-plane write in step S31 results from ashort circuit of the word line WLx+1 in the plane PB1.

In step S45, the data restore circuit 242 uses the memory read data A0obtained in step S43 and the restore data RA01 to restore the memoryread data A1 in the buffer 230.

In contrast, when the error correction of the memory read data A0 failsin step S43 (Yes branch), steps S46 and S47 are performed. The advanceof the flow to the Yes branch of step S43 may occur when the failure ofthe multi-plane write in step S31 results from a short circuit of theword line WLx+1 in plane PB0. Steps S46 and S48 are the same as stepsS12 and S13 of FIG. 10, respectively.

Specifically, in steps S46 and S48, the media controller 240 and thesequencer 12 perform a single plane read from the cell unit CUx of theplane PB1. The flow then shifts to step S48. Step S48 is the same asstep S14, and specifically the media controller 240 in step S48 tries toobtain correct memory read data A1. The obtaining of correct memory readdata should succeed. This is because the arrival at step S48 resultsfrom the failure of the write in step S31 due to the short circuit ofthe word line WLx+1 of the plane PB0, and, therefore, the memory readdata A1 in the cell unit CUx of the plane PB1 can be correctly read bythe single plane read.

In step S49, the data restore circuit 242 uses the memory read data A1obtained in step S48 and the restore data RA01 to restore the memoryread data A0 in the buffer 230.

The No branch of step S37 and steps S45 and S49 continues at step S38.In step S38, the media controller 240 and the sequencer 12 perform amulti-plane write to four cell units CU different from the cell unitsCUx and CUx+1 of the memory write data A0, A1, B0, and B1. Step S38 caninclude, for example, the flow of FIGS. 17 and 18. The media controller240, however, assigns cell units CU different from those assigned to thememory write data A0, A1, B0, and B1 in step S21 in the first loop, andthe flow of FIGS. 17 and 18 is performed for the newly assigned cellunits CU. For example, the host write data HA0 and HA1 are respectivelyassigned to the addresses of cell units CUy (y being zero or a naturalnumber smaller than or equal to n other than x) of the planes PB0 andPB1, and the host write data HB0 and HB1 are respectively assigned tothe addresses of cell units CUy+1 of the planes PB0 and PB1.

FIG. 19 illustrates the outline of a write in the memory system 1 of thesecond embodiment. The operations illustrated in FIG. 19 may occur bythe execution of the flow of FIGS. 17 and 18. FIG. 19(a) corresponds tostep S23, S24, S25, S27, S28, S29, S31, and the No branch of S32 of FIG.17. A multi-plane write to the cell unit CUx succeeds, and a multi-planewrite of cell unit CUx+1 fails.

FIG. 19(b) corresponds to step S34, S35, and the Yes branch of S37 ofFIG. 17. The media controller 240 performs a multi-plane read to thecell units CUx based on assumption of occurrence of a short circuitbetween the word lines WLx and WLx+1, but it fails.

FIG. 19(c) corresponds to the set of steps S41, S42 and the No branch ofS43, or the set of steps S41, S42, the Yes branch of step S43, and stepsS46, S47, and S48 of FIGS. 17 and 18. The media controller 240 performsa single plane read from each of the cell unit CUx of the plane PB0 andthat of the plane PB1.

FIG. 19(d) corresponds to the set of steps S45 and S38 or the set ofsteps S49 and S38 of FIG. 18. The media controller 240 uses asuccessfully-read one of the memory write data A0 and A1 and the restoredata RA01 to restore the other. The media controller 240 then writes thememory write data A0, A1, B0, and B1 into the cell units CUy and CUy+1of the planes PB0 and PB1.

FIG. 20 illustrates signals communicated between the memory controller200 and the memory device 100 during a multi-plane write in the memorysystem of the second embodiment over time. The communication in FIG. 20may occur in steps S23 and S29 of FIG. 17.

As illustrated in FIG. 20, the media controller 240 transmits a writecommand 80h, an address signal for the plane PB0, and memory write dataA0 (A00 to A0 j) to the memory device 100, where j is a natural number.After the media controller 240 transmits the memory write data A0 j, ittransmits a command 11h to the memory device 100. The command 11hinstructs not to start and to suspend the write specified by the command80h and the following address signal, and indicates a subsequentinstruction will follow. After the command 11h, the media controller 240transmits a write command 80h, an address signal for the plane PB1, andmemory write data A1 (A10 to A1 j) to the memory device 100. After themedia controller 240 transmits the data A1 j, it transmits a command 10hto the memory device 100. When the memory device 100 receives thecommand 10h, it performs the instructions. The execution of theinstructions corresponds to the execution of steps S24 and S31 of FIG.17, for example.

(Advantages)

Failure of a multi-plane write into a particular cell unit CUx+1 mayresult from various causes, and the cause of a failure cannot be easilyspecified immediately. In contrast, a failure of multi-plane write intothe cell units CUx+1 may disable a read of data from written cell unitsCUx of the plane PB0 and/or PB1 due to some causes. For example, whenthe word lines WLx+1 and WLx of the plane PB0 are short-circuited duringa multi-plane write into the cell units CUx+1 of the plane PB0, datacannot be read from the cell unit CUx of the plane PB0. To address this,it is possible that, when it is determined that a multi-plane write intothe cell units CUx+1 during successive multi-plane writes to plural cellunits CU fails, data which have become unreadable is restored to bewritten into another cell unit CU again. To this end, the memorycontroller 200 can perform a multi-plane read to the cell units CUx whenthe multi-plane write to the cell units CUx+1 fails. Such a multi-planeread may fail. This failure is unlikely to result from a short circuitin both respective word lines WLx of the two planes PB0 and PB1, asdescribed in the first embodiment.

The memory system 1 of the second embodiment performs a multi-plane readto the cell unit CUx when the write to the cell unit CUx+1 in successivemulti-plane writes to two adjacent cell units CUx and CUx+1 fails. Whenboth resultant read data are error-uncorrectable, the memory system 1performs a single plane read from each of the planes PB0 and PB1 as inthe first embodiment. This, even when data read from two planes PB witha multi-plane read fails due to a short circuit of the word line WLx ofone of the plane PB, enables the data to be correctly read from the cellunit CU of the word line WLx of the other plane PB. Even when the cellunit CUx of one plane PB0 cannot be read, the associated restore datamay remain in the buffer 230 in the case of successive multi-planewrites to plural cell units CU. In this case, the data in the cell unitCUx of the plane PB0 can be restored with the restore data and the datain the cell unit CUx of the other plane PB1.

Such restoration does not incur a large cost. Specifically, the use ofthe restore data obviates the need to store the associated entire twodata items for planes PB0 and PB1 in the buffer 230. Therefore, the useof restore data eliminates the necessity of storing (backup) of thewhole memory write data instructed to be written to cell units CU fromthe host device 1 until they are determined to be unnecessary by thestatus read. This is illustrated in FIGS. 21 and 22.

FIG. 21 illustrates a possible example of storing write data insuccessive multi-plane writes to cell units CUx and CUx+1 similarly tothe flow of FIGS. 17 and 18. As illustrated in FIG. 21, the memorycontroller maintains the memory write data A0, A1, B0, and B1 until thewrite into the cell unit CUx+1 is completed in case the word lines WLx+1and WLx are short-circuited during a write to the cell units CUx+1,which disables the read of data in the cell units CUx in a buffer.

FIG. 22 illustrates storing data with use of the second embodiment.According to the second embodiment, only the restore data RA01 andmemory write data B0 and B1 need to be maintained until the successivemulti-plane writes to the cell units CUx and CUx+1 succeed. This isbecause even with a short circuit in one plane PB, a single plane readallows data A0 or A1 written in the cell unit CUx of the other plane PBto be restored with the restore data RA01.

Third Embodiment

The third embodiment is similar to the second embodiment, and relates tothe version of the second embodiment with the multi-string type blocksBLK.

In the multi-string type case, one block BLK includes a total of fourcell units CUi each of which is from one of the four (with example ofk=3) string units SU and which are coupled to a particular word lineWLi, where i is zero or a natural number smaller than or equal to n.Such string units CUi from the string units SU0, SU1, SU2, and SU3 arereferred to as cell units CUi(0), CUi(1), CUi(2), and CUi(3),respectively.

In the third embodiment, the memory system 1 has the same functionalblocks as the memory system 1 of the first embodiment. The memorycontroller 200 in the third embodiment is, however, configured toperform the operations described in the following.

Referring to FIGS. 23 to 26, a write in the memory system of the thirdembodiment is described. FIGS. 23 and 24 illustrate a part of the flowof a write of the memory system of the third embodiment. When the hostdevice 2 instructs a write to the memory system 1 and the instructionleads to a multi-plane write, the flow of FIGS. 23 and 24 starts. As anexample, the overall controller 220 interprets the write instructionfrom the host device 2, and determines that it will write host writedata HA0, HB0, HC0, HD0, HE0, HF0, HG0, and HH0 into the plane PB0, andhost write data HA1, HB1, HC1, HD1, HE1, HF1, HG1, and HH1 to the planePB1. When this determination fulfills the following conditions, the flowof FIGS. 23 and 24 starts.

The host write data HA0, HB0, HC0, and HD0 will be written into cellunits CUi(0), CUi(1), CUi(2), and CUi(3) of the plane PB0, respectively.The host write data HE0, HF0, HG0, and HH0 will be written into cellunits CUi+1(0), CUi+1(1), CUi+1(2), and CUi+1(3) of the plane PB0,respectively. The host write data HA1, HB1, HC1, and HD1 will be writteninto cell units CUi(0), CUi(1), CUi(2), and CUi(3) of the plane PB1,respectively. The host write data HE1, HF1, HG1, and HH1 will be writteninto cell units CUi+1(0), CUi+1(1), CUi+1(2), and CUi+1(3) of the planePB1, respectively.

Reception of instruction of such conditions triggers the flow of FIGS.23 and 24. The flow of FIGS. 23 and 24 occurs after the instruction totrigger the flow of FIGS. 23 and 24 and before the performance (or,completion) of another additional instruction (or, request) from thehost device 2 by the memory system 1, for example. Specifically, theflow occurs as a response to reception of the write instruction of thehost write data HA0, HB0, HC0, HD0, HE0, HF0, HG0, HH0, HA1, HB1, HC1,HD1, HE1, HF1, HG1, and HH1.

In addition, the flow occurs as a response to reception of one writeinstruction of the host write data HA0, HB0, HC0, HD0, HE0, HF0, HG0,HH0, HA1, HB1, HC1, HD1, HE1, HF1, HG1, and HH1 from the host device 2.In other words, the flow is performed without reception of two or moreidentical instructions from the host device 2.

The outline of the flow of FIGS. 23 and 24 is substantially the same asthe flow of FIGS. 17 and 18, and differences are based on writes intocell units CU of the four string units SU in each plane PB in the thirdembodiment.

Steps S51, S54, S55, S56, S57, S58, S61, S62, S63, S64, S66, S67, S68,S70, S71, S73, and S74 are the same or similar to steps S21, S29, S31,S32, S33, S34 and S35, S41 and S42, S43, S45, S46 and S47, S48, S49,S38, S25, S27, S29, and S41 of FIGS. 17 and 18, respectively.Differences are mainly described in the following.

First, with steps S51 and S52, memory write data A0, B0, C0, D0, E0, F0,G0, H0, A1, B1, C1, D1, E1, F1, G1, and H1 are generated from the hostwrite data HA0, HB0, HC0, HD0, HE0, HF0, HG0, HH0, HA1, HB1, HC1, HD1,HE1, HF1, HG1, and HH1, and the memory write data A0, B0, C0, D0, E0,F0, G0, A1, B1, C1, D1, E1, F1, and G1 are written into the memorydevice 100, which succeeds as an example. Details are as follows.

In step S51, cell units CU into which the host write data will bewritten are determined as follows as in step S21 of FIG. 17.Specifically, the host write data HA0, HB0, HC0, and HD0 will be writteninto cell units CUx(0), CUx(1), CUx(2), and CUx(3) of the plane PB0,respectively. The host write data HE0, HF0, HG0, and HH0 will be writteninto cell units CUx+1(0), CUx+1(1), CUx+1(2), and CUx+1(3) of the planePB0, respectively. The host write data HA1, HB1, HC1, and HD1 will bewritten into cell units CUx(0), CUx(1), CUx(2), and CUx(3) of the planePB1, respectively. The host write data HE1, HF1, HG1, and HH1 will bewritten into cell units CUx+1(0), CUx+1(1), CUx+1(2), and CUx+1(3) ofthe plane PB1, respectively.

In step S52, multi-plane writes to same-address cell units CU forsame-address string units SU for same-address blocks BLK of the planesPB0 and PB1 are performed for all the host write data except the hostwrite data HH0 and HH1. A multi-plane write into same-address cell unitsCU for same-address string units SU includes execution of substeps S522,S523, S524, S525, and S527. Step S52 includes a repetition of executionof the set of substeps S522, S523, S524, S525, and S527. Substeps S522,S523, S524, S525, and S527 are the same or similar to steps S22, S23,S24, S25, and S27 of FIG. 17, respectively.

In substep S522, the media controller 240 generates the memory writedata A0 and A1 and restore data RA01 from the host write data HA0 andHA1.

In substep S523, the media controller 240 instructs a multi-plane writeof the memory write data A0 and A1 into the cell units CUx(0) to thememory device 100.

In substep S524, the sequencer 12 writes the memory write data A0 and A1into respective cell units CUx of the planes PB0 and PB1, respectively.

In substep S525, the media controller 240 reads the status of the memorydevice 100. Assume that the write succeeds in the ongoing example forsimplification of the description. In substep S527, the media controller240 stops storing of the memory write data A0 and A1, whereas itmaintains the restore data RA01.

Similarly, substeps S522 to S527 are repeated. As a result, the state ofFIG. 25 is reached. As illustrated in FIG. 25, the plane PB0 stores thememory write data A0, B0, C0, and D0 in the cell units CUx(0), CUx(1),CUx(2), and CUx(3), respectively. The plane PB0 stores the memory writedata E0, F0, and G0 in the cell units CUx+1(0), CUx+1(1), and CUx+1(2),respectively. The plane PB1 stores the memory write data A1, B1, C1, andD1 in the cell units CUx(0), CUx(1), CUx(2), and CUx(3), respectively.The plane PB1 stores the memory write data E1, F1, and G1 in the cellunits CUx+1(0), CUx+1(1), and CUx+1(2), respectively. The memory writedata A0, B0, C0, D0, E0, F0, G0, A1, B1, C1, D1, E1, F1, and G1 aregenerated from the host write data HA0, HB0, HC0, HD0, HE0, HF0, HG0,HA1, HB1, HC1, HD1, HE1, HF1, and HG1, respectively. The mediacontroller 240 further stores restore data RA01, RB01, RC01, RD01, RE01,RF01, and RG01 in the buffer 230. The restore data RX01 (X being B, C,D, E, F, or G) allows one of the memory read data X0 and X1 to berestored when used with the other.

Referring back to FIG. 23, step S52 shifts to step S53. In step S53, themedia controller 240 generates memory write data H0 and H1 and restoredata RH01 from the host write data HH0 and HH1. The restore data RH01allows one of the memory read data H0 and H1 to be restored when usedwith the other.

In step S54, the media controller 240 instructs a multi-plane write ofthe memory write data H0 and H1 into the cell units CUx+1(3) to thememory device 100.

In step S55, the sequencer 12 writes the memory write data H0 and H1 inrespective cell units CUx+1(3) of the planes PB0 and PB1, respectively.

In step S56, the media controller 240 reads the status of the memorydevice 100. When the result of status read indicates a success (Yesbranch), the media controller 220 erases the memory write data H0 and H1from the buffer 230 in step S57. Moreover, the overall controller 220notifies the completion of the instruction to the host device 2, wherethe flow ends.

In contrast, the determination of the failure of the write in step S56(No branch) may occur due to occurrence of a short circuit between theword lines WLx+1 and WLx during the writes to the cell units CUx+1(3) ofthe planes PB0 and PB1 in step S54. The following description is basedon an example where the word lines WLx+1 and WLx of the plane PB0 areshort-circuited. With the failure of the write, the flow shifts to stepS58.

In step S58, the media controller 240 and the sequencer 12 performmulti-plane reads from one of the cell units CUx(0), CUx(1), CUx(2) andCUx(3). The following description is based on an example of a read fromthe cell unit CUx(0), i.e., the memory read data A0 and A1 are read. Themulti-plane read instruction includes specification of a string unit SU.

Step S59 is similar to step S37. In step S59, the media controller 240tries to obtain the correct memory read data A0 and A1. Assume thatobtaining the memory read data A0 and A1 fails in the ongoing examplefor simplification of the description. Such failure may result fromshort-circuiting between the word lines WLx+1 and WLx and execution of amulti-plane read.

In step S61, the media controller 240 and the sequencer 12 perform asingle plane read from the cell unit CUx(0) of the plane PB0. The singleplane read instruction includes specification of a string unit SU.

In step S62, the media controller 240 tries to obtain the correct memoryread data A0. When the obtaining succeeds (No branch), the flow shiftsto step S63. In step S63, the media controller 240 restores the memoryread data A1.

When the obtaining at step S62 fails (Yes branch), the flow shifts tostep S64. In step S64, the media controller 240 and the sequencer 12perform a single plane read from the cell unit CUx(0) of plane PB1. Thesingle plane read instruction includes specification of a string unitSU.

In step S66, the media controller 240 tries to obtain correct memoryread data A1. The obtaining should succeed because the word lines WLx+1and WLx are short-circuited in the ongoing example as described above.

In step S67, the media controller 240 restores the memory read data A0.

In step S68, the media controller 240 and the sequencer 12 perform amulti-plane write of the data A0 and A1 into cell units CUy(0) of theplanes PB0 and PB1. Assume that the write succeeds in the ongoingexample for simplification of description (step S70). Subsequently, thestoring of the memory write data A0 and A1 ends in step S71.

In step S72, reads of the remaining written memory read data in the cellunits CUx and Cux+1, restoration, and writes into other cell units CUyor CUy+1 are performed. Specifically, step S72 includes repetition ofthe execution of the set of substeps S721, S722, S723, S724, and S726for the memory read data B0, C0, D0, E0, F0, G0, B1, C1, D1, E1, F1, andG1. Substeps S721, S722, S723, S724, S725, and S726 are the same as orsimilar to steps S46 and S47, S48, S49, S38, S25, and S27, respectively.In the following, substeps S721, S722, S723, S724, S725, and S726 aredescribed concerning an example for the memory read data B0 and B1.

In substep S721, the media controller 240 and the sequencer 12 read thememory read data B1 from the cell unit CUx(1) of the plane PB1. Thereason for the read from plane PB1 is that the short-circuit between theword lines WLx and WLx+1 of the plane PB0 is determined by step S62.

In substep S76, the media controller 240 obtains the correct memory readdata B1.

In substep S723, the media controller 240 restores the read data B0 fromthe read data B1.

In substep S724, the media controller 240 and the sequencer 12 perform amulti-plane write of the memory read data B0 and B1 to the cell unitsCUy(1) of the planes PB0 and PB1. Assume that the write succeeds in theongoing example for simplification of the description (substep S725).Subsequently, storing of the memory write data B0 and B1 ends in substepS726.

As a result of step S72, the state illustrated in FIG. 26 is reached. Asillustrated in FIG. 26, the plane PB0 stores the memory write data A0,B0, C0, and D0 in the cell units CUy(0), CUy(1), CUy(2), and CUy(3),respectively. The plane PB0 stores the memory write data E0, F0, and G0in the cell units CUy+1(0), CUy+1(1), and CUy+1(2), respectively. Theplane PB1 stores the memory write data A1, B1, C1, and D1 in the cellunits CUy(0), CUy(1), CUy(2), and CUy(3), respectively. The plane PB1stores the memory write data E1, F1, and G1 in the cell units CUy+1(0),CUy+1(1), and CUy+1(2), respectively.

Referring back to FIG. 24, step S72 continues at step S73. In step S73,the media controller 240 instructs a multi-plane write of the memorywrite data H0 and H1 into the cell units CUy+1(3) to the memory device100.

In step S74, the sequencer 12 writes the memory write data H0 and H1into the select cell units CUy+1(3) of the planes PB0 and PB1,respectively.

In step S76, the status is read. Assume that the write succeeds forsimplification of the description. Step S76 continues at step S57.

(Advantages)

When the memory system 1 of the third embodiment fails a write in cellunits CUx+1 in successive multi-plane writes in the cell units CUx andCUx+1, it performs a multi-plane read to the written cell units CUx, asin the second embodiment. When both of resultant read data areerror-uncorrectable, the memory system 1 performs a single plane readfrom each of the planes PB0 and PB1. Such a single plane read isperformed to all the cell units CU written in writes by a series ofwrite instructions. This produces the same advantages as the secondembodiment also with the multi-string type. In addition, the memorysystem 1 performs single plane reads from all the cell units CUx+1 in aplane PB where the current does not leak from the word line WLx+1 (forexample, plane PB1) written by a series of write instructions. For thisreason, written data in a plane PB without a current leak in the wordline WLx+1 can be read even when they cannot be read with a multi-planeread.

With such reads, the capacity of the buffer 230 for backup of memorywrite data can be reduced greatly in the multi-string type. This isillustrated in FIGS. 27 and 28. FIG. 27 illustrates a possible exampleof storing write data in the successive multi-plane writes to cell unitsCUx(0) to CUx(3) and CUx+1(0) to CUx+1(3) similarly to the flow of FIGS.23 and 24. As illustrated in FIG. 27, the memory controller stores thememory write data A0, B0, C0, D0, E0, F0, G0, H0, A1, B1, C1, D1, E1,F1, G1, and H1 until the write to the cell units CUx+1(3) is completedin case the word lines WLx+1 and WLx are short-circuited during a writeto the cell units CUx+1, which disables the read of data in the cellunits CUx(0) to CUx(3) in a buffer.

FIG. 28 illustrates storing data with use of the third embodiment.According to the third embodiment, in successive multi-plane writes tothe cell units CUx and CUx+1, only the restore data RA01, RB01, RC01,RD01, RE01, RF01, and RG01, and the memory write data H0 and H1 need tobe stored. The higher the number of string units SU per block BLK, themore the capacity required for the buffer 230 can be reduced.

Fourth Embodiment

In the fourth embodiment, a check on whether a current leaks due to ashort circuit is used.

In the fourth embodiment, the memory system 1 has the same functionalblocks as the memory system 1 of the first embodiment except for themedia controller 240. Specifically, as illustrated in FIG. 29, the mediacontroller 240 includes a leak word line table 243 in addition to thefunctional blocks in the first embodiment. Based on this, the memorycontroller 200 is configured to perform the operations described in thefollowing in the fourth embodiment. Moreover, the blocks BLK of thefourth embodiment are of the single string type.

The leak word line table 243 indicates correspondences between a pair ofshort-circuited word lines WL and a plane to which the pair of wordlines WL belong, as illustrated in FIG. 30. The pair of short-circuitedword lines WL is specified by a status read after a multi-plane write,for example. The leak word line table 243 is appropriately updatedduring operations of the memory system 1 as will be described, stored inthe memory device 100 when the power supply of the memory system 1 isstopped, and read from the memory device 100 into the RAM in the memorycontroller 200 upon the next power supply.

Referring to FIGS. 31 to 35, a write in the memory system of the fourthembodiment will now be described. FIGS. 31 and 32 illustrate the flow ofa write in the memory system of the fourth embodiment. When the hostdevice 2 instructs a write to the memory system 1 and the instructionleads to a multi-plane write, the flow of FIGS. 31 and 32 starts. As anexample, the overall controller 220 determines that it will write hostwrite data HA0 and HA1 into same-address cell units CU of the planes PB0and PB1, respectively. When the determined instruction is received bythe media controller 240, the flow of FIGS. 31 and 32 starts. The flowof FIGS. 31 and 32 occurs after the instruction to trigger the flow ofFIGS. 31 and 32 and before the performance (or, completion) of anotheradditional instruction (or, request) from the host device 2 by thememory system 1. Specifically, the flow occurs as a response toreception of the write instruction of the host write data HA0, HA1, HB0,and HB1. In addition, the flow occurs as a response to reception of onewrite instruction of the host write data HA0, HA1, HB0, and HB1 from thehost device 2. In other words, the flow is performed without receptionof two or more identical instructions from the host device 2.

When the flow starts, it shifts to step S81. Step S81 is similar to stepS21 of FIG. 17. In step S81, the media controller 240 determines that itwill write the host write data HA0 and HA1 into cell units CUx of theplanes PB0 and PB1, respectively.

Steps S82, S83, and S84 are the same as steps S22, S23, and S24respectively.

In step S85, the sequencer 12 checks whether the write in both planesPB0 and PB1 fails. The test is conducted by execution of a so-calledverification. Specifically, it is determined how much data read from thecell unit CUx of the plane PB0 and the memory write data A0 match andhow much the data read from the cell unit CUx of the plane PB1 and thememory write data A1 match. In each plane PB, it is determined that thewrite in this plane PB fails when the degree of matching is below aparticular criteria. When the writes in both planes PB0 and PB1 succeed(No branch), the flow shifts to step S87.

In step S87, the sequencer 12 sets information indicative of completionof the instruction of step S83 in the register 13.

In contrast, when the writes in both planes PB0 and PB1 fail (Yes branchof step S85), the flow shifts to step S88. In step S88, the sequencer 12performs a current leak test for each word line WLx of the planes PB0and PB1. The sequencer 12 performs the current leak test to determinewhether a current is leaking from the word lines WLx of planes PB0and/or PB1. The current leak test will be described later. Assume thatin order to simplify the description, current leaks in the ongoingexample.

The sequencer 12 sets in the register 13 the address of the word lineWLx, and information to specify the plane PB0 and/or PB1 including theword line WLx in step S90. The following description is based on anexample where a current leaks in the plane PB0.

Step S90 continues at step S91. Step S87 also continues at step S91. Instep S91, the media controller 240 uses a status read command XXh toread the status of the memory device 100. The example of the read statusdata is illustrated in FIG. 33. As illustrated in FIG. 33, the statusdata indicates, in addition to the same types of information as those inFIG. 16, whether the planes PB0 and PB1 which include the cell units CUxspecified just before in I/O[2] and I/O[3] generate a leak current,respectively.

When step S91 follows step S87, the status data indicates a success ofthe multi-plane write. When step S91 follows step S90, the status dataindicates a failure of the multi-plane write and occurrence of currentleak in planes PB0 and/or PB1 (plane PB0 in the ongoing example).

Referring back to FIG. 32, when the result of the status read indicatesa success of the write (Yes branch of step S92), the flow shifts to stepS93. In step S93, the overall controller 220 notifies the host device 2of the completion of the instruction, where the flow ends.

In contrast, when the result of the status read indicates a failure ofthe write (No branch of step S92), the flow shifts to step S94. In stepS94, the media controller 240 determines whether a current leaks fromthe word line WLx with reference to the status data. When the occurrenceof current leak is not indicated (No branch), this means that thefailure of the multi-plane write does not result from the current leakin the word line WLx. Based on this, the media controller 240 and thesequencer 12 write the memory write data A0 and A1 in cell units CUy instep S95. Step S95 continues at step S93.

In contrast, when in step S94 the occurrence of current leak isindicated (Yes branch), the flow shifts to step S97. In step S97, themedia controller 240 registers in the leak word line table 243 an entryincluding the set of the addresses of the pair of word lines WLx andWLx−1 between which a current leaks, and the address of the plane PBincluding those word lines WL. Step S97 continues at step S95.

Referring to FIG. 34, detection of a leak current will now be described.FIG. 34 illustrates voltages applied to some interconnects duringdetection of current leak of a selected word line WL (WLx) of aparticular block BLK of a particular plane over time.

A signal Flag is an internal signal of the charge pump 14, and providedfor a pump unit 141 p of pump units 141 which outputs the potentialVPGM. The signal Flag has a logic based on a target voltage, which thepump unit 141 p should output. The pump unit 141 p compares the outputvoltage thereof with the target voltage, and when the output voltageexceeds the target voltage, it makes the signal Flag low to stop theoperation for raising output voltage. Therefore, the signal Flag can beused as an index to indicate whether the output voltage of the pump unit141 p exceeds the target voltage.

The occurrence of current leak can be detected by monitoring the signalFlag during application of the write voltage to the test target wordline WLx. An example is as follows.

The driver set 11 uses a potential VSGD supplied from the charge pump 14to keep applying a voltage VSGD to a select gate line SGDL during awrite from time t0. The voltage VSGD has a magnitude to turn on theselect transistor SDT.

From time t1, the driver set 11 uses a potential VPASS supplied from thecharge pump 14 to apply a voltage VPASS to unselected word lines WL. Thevoltage VPASS has a magnitude which turns on the cell transistors MT andallows all the cell transistors MT between the cell transistor MT of theword line WLx and the select gate line SGDL to transfer the potential ofthe bit line BL. The application of the voltage VPASS to the unselectedword lines WL continues until time t4. The voltage VPASS is applied alsoto the selected word line WL from time t1.

The driver set 11 uses the potential VPGM supplied from the charge pump14 to apply a voltage VPGM to the selected word line WL from time t2 totime t3. The voltage VPGM is higher than the voltage VPASS. At time t3,the driver set 11 drops the voltage applied to the word line WLx to thevoltage VPASS. At time t4, the driver set 11 decreases the voltageapplied to all the word lines WL back to 0V.

The output of the pump unit 141 p should exceed the voltage VPGM atleast once between time t2 and t3. For this reason, the signal Flagshould transition to low at least once between time t2 and time t3. Incontrast, with the word line WLx leaking a current, the output of thepump unit 141 p does not reach voltage VPGM between time t2 and time t3.For this reason, with the selected word line WL leaking a current, thesignal Flag remains high from time t2 and time t3. This characteristiccan be used to detect a current leak from the word line WLx throughmonitoring the signal Flag.

FIG. 35 illustrates the outline of a write in the memory system 1 of thefourth embodiment. The operation illustrated in FIG. 35 may occur by theexecution of the flow of FIGS. 31 and 32. FIG. 35(a) corresponds tosteps S83, S84, and the Yes branch of S85 of FIG. 31. A multi-planewrite to the cell unit CUx fails.

FIG. 35(b) corresponds to steps S88, S90, S91, S92, S94, and S97 of FIG.31. The memory device 100 performs a current leak test to determinewhether a current leaks from the word lines WL of the planes PB0 and/orPB1. When leaking, the media controller 240 updates the leak word linetable 243.

FIG. 35(c) corresponds to step S95 of FIG. 31. The media controller 240and the sequencer 12 write the memory write data A0 and A1 in the cellunits CUy of the planes PB0 and PB1.

Referring to FIG. 36, a read in the memory system of the fourthembodiment will now be described. FIG. 36 illustrates the flow of a readin the memory system of the fourth embodiment. When the host device 2instructs a read to the memory system 1 and the instruction leads to amulti-plane read, the FIG. 36 flow starts. As an example, theinstruction instructs a read of host read data HA0 and HA1, and thisleads to a read of memory read data A0 and A1 from cell units CUx−1 ofthe planes PB and PB1. The FIG. 36 flow occurs after the instruction totrigger the FIG. 36 flow and before the performance (or, completion) ofanother additional instruction (or, request) from the host device 2 bythe memory system 1, for example. Specifically, the flow occurs as aresponse to reception of the read instruction of the host read data HA0and HA1. In addition, the flow occurs as a response to reception of oneread instruction of the host read data HA0 and HA1 from the host device2. In other words, the flow is performed without reception of two ormore identical instructions from the host device 2.

When the flow starts, the media controller 240 in step S101 determineswhether the address of a word line WLx−1 is included in the leak wordline table 243. When not included (No branch), the flow shifts to stepS102. Step S102 is similar to step S2. In step S102, the mediacontroller 240 instructs a multi-plane read from cell units CUx−1 to thememory device 100.

Step S103 is similar to step S3. In step S3, the sequencer 12 reads thememory read data A0 and A1 from the cell units CUx−1.

Step S104 is similar to step S4. In step S104, the media controller 240tries to obtain the correct memory read data A0 and A1. Assume that theobtaining succeeds in the ongoing example for simplification of thedescription.

Step S105 is similar to step S5. In step S105, the overall controller220 transmits the host read data HA0 and HA1 to the host device 2, wherethe flow ends.

In contrast, when the result of determination in step S101 indicatesthat the address of the word line WLx−1 is included (Yes branch), theflow shifts to step S111. In step S111, the media controller 240 refersto the leak word line table 243 to learn the address of the plane PBincluded in the entry which includes the address of the word line WLx−1.Assume that in the following example the entry indicates the plane PB0,i.e., the current leak in the word line WLx−1 occurs in the plane PB0.

Step S112 is similar to steps S7 and S12. In step S112, the mediacontroller 240 instructs, to the memory device 100, a single plane readfrom the cell unit CUx−1 of the plane PB1, in which a current does notleak in the word line WLx−1.

Step S113 is similar to steps S8 and S13. In step S113, the sequencer 12reads the memory read data from the cell unit CUx−1 of the instructedplane PB (A1 in the ongoing example).

In step S114, the media controller 240 tries to obtain correct memoryread data A1 as in, for example, step S4. Assume that the obtainingsucceeds in the ongoing example for simplification of the description.Moreover, the media controller 240 restores the memory read data A0. Therestoration can be performed by any method, and, for example, with aproduct code generated using the memory read data A0 and other memoryread data used to generate the product code with the memory read A0.Step S114 continues at step S105.

(Advantages)

In the fourth embodiment, when a multi-plane write to a selected cellunits CU fails, it is determined whether a current leaks from theselected word lines WL in planes PB0 and/or PB1. When leaking, the mediacontroller 240 registers in the leak word line table 243 the set of theaddresses of a pair of the word line WLx and the word line WLx−1 withone smaller address, and the address of the plane PB to which the pairbelong. Then, when the media controller 240 receives an instructionwhich leads to a multi-plane read from the host device 2, it determineswhether the selected word lines WL−1 is included in the leak word linetable 243. When included, the media controller 240 performs a singleplane read from the cell unit CUx−1 of the plane PB different from theplane PB to which the word line WLx−1 belongs.

As described in the first embodiment, a failure of reading data fromboth the planes PB in a multi-plane read may result from current leak ofthe selected word line WL in one plane PB. Based on this, the address ofthe plane PB which suffers from the current leak is registered in theleak word line table 243 when a multi-plane write fails, and, when themedia controller 240 receives a following instruction which leads to amulti-plane read, it performs a single plane read to the plane PB whichdoes not suffer from the current leak. As a result, execution of thesingle plane read after it is learned that a multi-plane read fails isavoided, and the efficiency of read is high.

Fifth Embodiment

The fifth embodiment is similar to the fourth embodiment, and relates tothe version of the fourth embodiment with multi-string type blocks BLK.

In the fifth embodiment, the memory system 1 has the same functionalblocks as the memory system 1 of the fifth embodiment. The memorycontroller 200 is, however, configured to perform the operationsdescribed in the following in the fifth embodiment.

Referring to FIGS. 37 to 39, a write in the memory system of the fourthembodiment will be described. FIGS. 37 and 38 illustrate the flow of awrite in the memory system of the fifth embodiment. When the host device2 instructs a write to the memory system 1 and the instruction leads toa multi-plane write, the flow of FIGS. 37 and 38 starts. As an example,the overall controller 220 determines that it will write host write dataHA0 and HA1 into same-address cell units CUx(z) of the planes PB0 andPB1, where z is zero or a natural number smaller than or equal to k(=3).When the determined write instruction is received by the mediacontroller 240, the flow of FIGS. 37 and 38 starts.

With the reception the instruction, the flow of FIGS. 37 and 38 starts.The flow of FIGS. 37 and 38 occurs after the instruction to trigger theflow of FIGS. 37 and 38 and before the performance (or, completion) ofanother additional instruction (or, request) from the host device 2 bythe memory system 1, for example. Specifically, the flow occurs as aresponse to reception of the write instruction of the host write dataHA0 and HA1. In addition, the flow occurs as a response to reception ofone write instruction of the host write data HA0 and HA1 from the hostdevice 2. In other words, the flow is performed without reception of twoor more identical instructions from the host device 2. The outline ofthe flow of FIGS. 37 and 38 is substantially the same as the flow ofFIGS. 31 and 32, and differences are that an instruction of multi-planewrite includes specification of a string unit SU to which the selectedcell units CU belong to and details of a current leak test.

Steps S121, S122, S123, S124, S125, S128, S130, S131, S132, S133, S134,S135, and S137 are the same as or similar to steps S81, S82, S83, S84,S85, S88, S90, S91, S92, S93, S94, S95, and S97 of FIGS. 31 and 32,respectively. Differences are mainly described in the following.

In steps S123 and S124, the media controller 240 and the sequencer 12instruct and perform a multi-plane write of memory write data A0 and A1into the cell units CUx(z) of the planes PB0 and PB1.

Voltages illustrated in FIG. 39 are applied during a current leak testin step S128. FIG. 39 is similar to FIG. 34, and time t10 to t14corresponds to time t0 to t4. Differences are that the driver set 11applies the voltage VSGD to the select gate line SGDL of the string unitSU(k) and keeps applying the voltage VSGS to the select gate line SGSLof the string unit SU(k) and the select gate lines SGDL and SGSL of theunselected string units SU during the test.

Referring to FIG. 40, a read in the memory system of the fifthembodiment will be described. FIG. 40 illustrates the flow of a read inthe memory system of the fifth embodiment. When the host device 2instructs a read to the memory system 1 and the instruction leads to amulti-plane read, the FIG. 40 flow starts. As an example, theinstruction instructs a read of host read data HA0 and HA1, which leadsto a read of memory read data A0 and A1 from cell units CUx−1(z) of theplanes PB0 and PB1. The FIG. 40 flow occurs after the instruction totrigger the FIG. 40 flow and before the performance (or, completion) ofanother additional instruction (or, request) from the host device 2 bythe memory system 1, for example. Specifically, the flow occurs as aresponse to the reception of the read instruction of the host read dataHA0 and HA1. In addition, the flow occurs as a response to reception ofone read instruction of the host read data HA0 and HA1 from the hostdevice 2. In other words, the flow is performed without reception of twoor more identical instructions from the host device 2.

Steps S141, S142, S143, S144, S145, S151, S152, S153, and S154 are thesame or similar to steps S101, S102, S103, S104, S105, S111, S112, S113,and S114, respectively. Differences are described in the following.

In steps S142 and S143, the media controller 240 and the sequencer 12instruct and perform a multi-plane read of the memory read data A0 andA1 from the cell units CUx−1(z) of the planes PB0 and PB1.

In steps S152 and S153, the media controller 240 and the sequencer 12instruct and perform a single plane read from the cell unit CUx−1(z) ofthe plane PB in which a current does not leak from the word line WLx−1(for example, the plane PB1).

(Advantages)

When a multi-plane write to cell units CU fails, the memory system 1 ofthe fifth embodiment tests a current leak and registers the set ofaddresses of the pair of word lines WL and the plane PB into the leakword line table 243 when leaking, as in the fourth embodiment. Then,when the address of the word line WLx−1 is included during a multi-planeread from cell units CUx−1, the media controller 240 performs a singleplane read from the cell unit CUx−1 of the plane PB different from theplane PB to which the word line WLx−1 belongs. This produces the sameadvantages as the fourth embodiment also with the multi-string type.

Sixth Embodiment

The sixth embodiment relates to detection of current leak.

In the sixth embodiment, the memory system 1 has the same functionalblocks as the memory system 1 of the first embodiment. In contrast, thememory device 100 is configured to perform operations described in thefollowing in the sixth embodiment.

The sequencer 12 performs the detection of current leak of the sixthembodiment due to various causes. The current leak detection of thesixth embodiment is performed, for example, as the current leakdetection in the fourth or fifth embodiment, or is triggered by aninstruction of the memory controller 200.

The basis of the current leak detection is the same as that describedwith reference to FIGS. 34 and 39. Differences are in the detection ofnot only the occurrence of the current leak but also the magnitudethereof. FIG. 41 illustrates voltages applied to some interconnectsduring detection of current leak of a selected word line WL (WLx) of aparticular block BLK of a particular plane over time, and is similar toFIG. 34.

A leak current from the target word line WLx may have variousmagnitudes. For example, the magnitude of a leak current is based on themagnitude of the resistance of a current path between the word line WLxand an adjacent WLx−1 (or WLx+1) formed by short circuit between theword lines WLx and WLx−1. The larger the current path due to the shortcircuit, the larger the leak current. The larger the leak current, thelonger the signal Flag is low or the higher the number of low signalFlag. FIG. 41 illustrates signals Flag for cases of leak currents ofthree different magnitudes.

The sequencer 12 measures a period for which the signal Flag of the pumpunit 141 p outputting voltage VPGM is high between time t2 and t3, andcalculates a ratio between the measured period and the period betweentime t2 and t3. When the signal Flag is high between time t2 and t3 fora first period, the sequencer 12 determines that a large current leaks.The first period is, for example, larger than 90% and smaller than orequal to 100% of the period between time t2 and t3. When the signal Flagis high between time t2 and t3 for a second period, the sequencer 12determines that a medium current leaks. The second period is shorterthan the first period, and, for example, larger than 80% and smallerthan or equal to 90% of the period between time t2 and t3. When thesignal Flag is high between time t2 and t3 for a third period, thesequencer 12 determines that a small current leaks. The third period isshorter than the second period, and, for example, larger than 70% andsmaller than or equal to 80% of the period between time t2 and t3. Whenthe signal Flag is high between time t2 and t3 for a fourth period, thesequencer 12 determines that no current leaks. The fourth period isshorter than the third period, and, for example, smaller than or equalto 70% of the period between time t2 and t3. Two or four or moreclassifications can be used instead of three.

The information on the magnitude (or classification) of the current leakis reflected in the status data transmitted by a status read commandXXh. FIG. 42 illustrates an example of information read by the statusread command XXh. The status data indicates, in addition to the sametypes of information as those in FIG. 16, whether the planes PB0 and PB1which include the cell units CUx specified just before generate currentleak, and class to which the magnitude of the leak current belongs inI/O[2] to I/O[7]. Specifically, I/O[2] and I/O[3] indicate that a largecurrent leaks in planes PB0 and PB1, respectively. I/O[4] and I/O[5]indicate that a medium current leaks in the planes PB0 and PB1,respectively. The medium current leak is smaller than a current leak incases indicated by I/O[2] and I/O[3]. I/O[6] and I/O[7] indicate that asmaller current leaks in the planes PB0 and PB1, respectively. The smallcurrent leak is smaller than a current leak in cases indicated by I/O[4]and I/O[5].

The memory controller 200 uses the status read to learn the magnitude ofthe current leak of particular word lines WL of plane PB0 and/or PB1.The memory controller 200 can control the memory device 100 based on thelearned magnitude of current leak. For example, a cell unit CU of a wordline WL from which a small current leaks due to a short circuit with anadjacent word line WL can output data. When such a cell unit CU is arepeatedly targeted for a read and/or write, this may worsen the shortcircuit and disable a read from that cell unit CU. Based on this, thememory controller 200 can use a word line WL with a small current leakless or, for example, assign such a word line WL to particular hostwrite data less than other word lines WL.

Other Embodiments and Additional Features

The description so far is based on examples of storing of one bit datain one cell transistor MT, i.e., storing of data of one-page size in onecell unit CU. The first to fifth embodiments are also applicable to acase of storing of data of two or more bits in one cell transistor MT,i.e., storing of data of a size of two or more pages in one cell unitCU. In this case, specification of where a write and a read will beperformed includes, in addition to specification of a cell unit CU,specification of a page in the specified cell unit CU. For example, fora case of storing of two pages in one cell unit CU, an upper page or alower page is specified.

During a flow of an embodiment, a process by another instruction fromthe host device 2 may be inserted. For such operations, the memorycontroller 200, in particular the overall controller 220, manages theorder or progress of such operations. For example, when the correctmemory read data cannot be obtained with a multi-plane read in step S4of FIG. 10, another process can be performed before step S7 andsubsequent steps are performed.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel methods and systems describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the methods andsystems described herein may be made without departing from the spiritof the inventions. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the inventions.

What is claimed is:
 1. A memory system comprising: a memory deviceincluding a first set of cell transistors coupled to a first word line,a second set of cell transistors coupled to a second word line, a thirdset of cell transistors coupled to a third word line adjacent to thefirst word line, and a fourth set of cell transistors coupled to afourth word line adjacent to the second word line; and a controllerconfigured to transmit to the memory device a first instruction whichinstructs parallel writes to the first and second sets of celltransistors, transmit to the memory device a second instruction whichinstructs transmission of a signal indicative of a state of the memorydevice to the memory device after transmission of the first instruction,receive a response to the second instruction, and transmit, when a firstrequest which requests reads from the third and fourth sets of celltransistors is received after reception of the response, a thirdinstruction which instructs a read from the third set of celltransistors or a fourth instruction which instructs a read from thefourth set of cell transistors.
 2. The system according to claim 1,wherein: the response indicates first information or second information,and the controller is configured to transmit the fourth instruction tothe memory device when the response indicates the first information andto transmit the third instruction to the memory device when the responseindicates the second information in response to the first request. 3.The system according to claim 2, wherein the memory device is configuredto test current leak between the first and third word lines, and currentleak between the second and fourth word lines before transmission of theresponse.
 4. The system according to claim 3, wherein: the firstinformation indicates current leak between the first and third wordlines, and the second information indicates current leak between thesecond and fourth word lines.
 5. The system according to claim 4,wherein the controller is configured to store at least one of the firstand second information and to transmit the third or fourth instructionbased on the stored first or second information in response to the firstrequest.
 6. The system according to claim 2, wherein: the memory devicefurther includes a charge pump configured to output a potential to beapplied to the first word line during a write to the first set of celltransistors, and is configured to generate a first signal having a firststate for a period for which a potential of an output of the charge pumpexceeds a first potential and determine a magnitude of current leakbetween the first and third word lines based on a length of a period inwhich the first signal is in the first state during a test of currentleak between the first and third word lines.
 7. The system according toclaim 6, wherein the memory device is configured to transmit informationbased on the determined magnitude of current leak to the controller. 8.The system according to claim 3, wherein: the memory device furtherincludes a charge pump configured to output a potential to be applied tothe first word line during a write to the first set of cell transistors,and is configured to generate a first signal having a first state for aperiod for which a potential of an output of the charge pump exceeds afirst potential and detect current leak between the first and third wordlines based on the first signal.
 9. The system according to claim 4,wherein the controller is configured to include a leak word line tablestoring the first and second information and to update at least one ofthe first and second information in the leak word line table whenreceiving the response to the second instruction.
 10. The systemaccording to claim 9, wherein the controller is configured to refer tothe leak word line table, when the first request is received afterreception of the response.
 11. A method of controlling a memory deviceincluding a first set of cell transistors coupled to a first word line,a second set of cell transistors coupled to a second word line, a thirdset of cell transistors coupled to a third word line adjacent to thefirst word line, and a fourth set of cell transistors coupled to afourth word line adjacent to the second word line, including:transmitting to the memory device a first instruction which instructsparallel writes to the first and second sets of cell transistors;transmitting to the memory device a second instruction which instructstransmission of a signal indicative of a state of the memory device tothe memory device after transmission of the first instruction; receivinga response to the second instruction; and transmitting, when a firstrequest which requests reads from the third and fourth sets of celltransistors is received after reception of the response, a thirdinstruction which instructs a read from the third set of celltransistors or a fourth instruction which instructs a read from thefourth set of cell transistors.
 12. The method according to claim 11,wherein: the response indicates first information or second information,and the fourth instruction is transmitted to the memory device when theresponse indicates the first information and the third instruction istransmitted to the memory device when the response indicates the secondinformation in response to the first request.
 13. The method accordingto claim 12, wherein: the first information indicates current leakbetween the first and third word lines, and the second informationindicates current leak between the second and fourth word lines.
 14. Themethod according to claim 13, further comprising storing at least one ofthe first and second information, wherein the third or fourthinstruction is transmitted based on the stored first or secondinformation in response to the first request.
 15. The method accordingto claim 13, further comprising: storing at the controller a leak wordline table storing the first and second information; and updating atleast one of the first and second information in the leak word linetable when receiving the response to the second instruction.
 16. Themethod according to claim 15, further comprising referring to the leakword line table when the first request is received after reception ofthe response.